/// 
        /// 打开子菜单        /// 可以判断是否被打开,已经被打开则激活        /// 
        /// typeof(From)获取子菜单类型        private void OpenChildForm(Type childType)//传进子窗口的类型,如何获得类型呢?        {            bool isOpened = false;            foreach (Form child in this.MdiChildren)            {                if (child.GetType() == childType)                {                    child.Activate();                    isOpened = true;                    break;                }            }            if (!isOpened)            {                //动态创建form实例                Form frm = (Form)Activator.CreateInstance(childType);                frm.MdiParent = this;                frm.WindowState = FormWindowState.Maximized;                frm.Show();            }        }